Pinacolato boronates (Bpin) with an empty p‐orbital on boron stabilize an adjacent carbon radical, in contrast to diethanolamino boronates [B(DEA)] where the boron is sp3‐hybridized. By alternately placing a pinacol or diethanolamine moiety on the boron atom, thus stabilizing or not stabilizing the corresponding adjacent radical, it is possible to control the behavior of α‐boronyl xanthates and construct a large variety of terminal or internal boronates in a modular fashion. The remarkable tolerance of polar groups and the ability to introduce quaternary centers are particularly noteworthy features of this process.
A modular approach to substituted cyclobutylboronic esters is described. It proceeds by successive intermolecular radical additions of xanthates to pinacolato 1‐cyclobutenylboronate and to pinacolato bicyclo[1.1.0]but‐1‐ylboronate. Success hinges on tuning the stability of the α‐boryl radical by exploiting the stabilizing influence of the trivalent boronic ester and the slightly destabilizing cyclobutane, which increases the σ‐character of the radical. Reductive removal of the xanthate group finally provides a range of 1,2‐ and 1,3‐disubstituted cyclobutylboronic esters. The contrast with cyclopropylboronic esters is striking, since the strong destabilization by the highly strained cyclopropane ring allows the first radical addition to take place but not the second. Furthermore, the first adducts are geminal xanthyl boronic esters that can be converted into cyclobutanones. This chemistry furnishes cyclobutylboronic esters that would be quite difficult to obtain otherwise and thus complements existing methods.
The ability of silicon to stabilize vinyl cationic species leads to a redox arylation of alkynes whereby the stringent limitations of reactivity and regioselectivity of alkyl‐substituted alkynes are lifted. This allows the synthesis of a range of α‐silyl‐α′‐arylketones under mild conditions in good to excellent yields and with high functional group tolerance, whereby the silicon moiety in the final products can either be removed for a formal acetone monoarylation transform, or capitalized upon for subsequent electrophilic substitutions at either side of the carbonyl group.
A modular, stereoselective route to trisubstituted (Z)-alkenyl (MIDA)boronates is described, consisting in the radical addition-fragmentation of dithiocarbonates to 2-(MIDA)boronyl-3-(2'-fluoro-pyridyl-6'-oxy)-alkenes. The bulky (MIDA)boronate ensures a highly stereoselective fragmentation that is enhanced by the poor stabilization of the radical adjacent to the tetravalent boron atom. The vinyl boronate precursors are prepared from propargyl alcohols by copper-catalyzed regioselective hydroborylation of their fluoropyridoxy derivatives, with the fluoropyridine acting as an internal directing group.The importance of organoboron compounds to organic synthesis, medicinal chemistry, and material sciences is overwhelming. 1 Indeed, the Suzuki-Miyaura cross-coupling ranks in the top five reactions used by medicinal chemists in drug discovery and development. 2 The stability, low toxicity, and versatile reactivity of organoboronates are considerable advantages that make them almost ideal synthetic intermediates.
A modular approach to substituted cyclobutylboronic esters is described. It proceeds by successive intermolecular radical additions of xanthates to pinacolato 1‐cyclobutenylboronate and to pinacolato bicyclo[1.1.0]but‐1‐ylboronate. Success hinges on tuning the stability of the α‐boryl radical by exploiting the stabilizing influence of the trivalent boronic ester and the slightly destabilizing cyclobutane, which increases the σ‐character of the radical. Reductive removal of the xanthate group finally provides a range of 1,2‐ and 1,3‐disubstituted cyclobutylboronic esters. The contrast with cyclopropylboronic esters is striking, since the strong destabilization by the highly strained cyclopropane ring allows the first radical addition to take place but not the second. Furthermore, the first adducts are geminal xanthyl boronic esters that can be converted into cyclobutanones. This chemistry furnishes cyclobutylboronic esters that would be quite difficult to obtain otherwise and thus complements existing methods.
Pinacolato boronates (Bpin) with an empty p-orbital on boron stabilizea na djacent carbon radical, in contrast to diethanolamino boronates [B(DEA)] where the boron is sp 3hybridized. By alternately placing apinacol or diethanolamine moiety on the boron atom, thus stabilizing or not stabilizing the corresponding adjacent radical, it is possible to control the behavior of a-boronyl xanthates and construct al arge variety of terminal or internal boronates in am odular fashion. The remarkable tolerance of polar groups and the ability to introduce quaternary centers are particularly noteworthy features of this process.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.
A modular approach to highly functional acyl (MIDA)boronates is described. It involves the generation of the hitherto unknown radical derived from acetyl (MIDA)boronate and its capture by various alkenes, including electronically unbiased, unactivated alkenes. In contrast to the anion of acetyl (MIDA)boronate, which has not so far been employed in synthesis, the corresponding radical is well behaved and readily produced from the novel α‐xanthyl acetyl (MIDA)boronate. This shelf‐stable, easily prepared solid is a convenient acyl (MIDA)boronate transfer agent that provides a direct entry to numerous otherwise inaccessible structures, including latent 1,4‐dicarbonyl derivatives that can be transformed into B(MIDA) substituted pyrroles and furans. A competition experiment indicated the acyl (MIDA)boronate substituted radical to be more stable than the all‐carbon acetonyl radical but somewhat less reactive in additions to alkenes.
Die Fähigkeit des Siliciums Vinylkationen zu stabilisieren führt zu einer Redoxarylierung von Alkinen, in der die strikte Limitierung von Reaktivität und Regioselektivität von alkyl‐substituierten Alkinen aufgehoben wird. Das erlaubt die Synthese einer Reihe von α‐Silyl‐α′‐arylketonen unter milden Bedingungen in guten bis exzellenten Ausbeuten und mit einer hohen Toleranz gegenüber anderen funktionellen Gruppen. Die Silicium‐Gruppe kann entweder für eine formale Monoarylierung von Aceton entfernt oder für weitere elektrophile Substitutionen auf beiden Seiten der Carbonyl‐Gruppe verwendet werden.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.